fix: add missing db import to resolve NameError in password update API

inventory-backend/app/api/v1/auth.py

@@ -1,6 +1,7 @@
 # app/api/v1/auth.py
 from flask import Blueprint, request, jsonify, current_app
 from flask_jwt_extended import jwt_required, get_jwt_identity
+from app.extensions import db
 from app.services.auth_service import AuthService
 from app.utils.decorators import permission_required, audit_log